Exhaust heating device for internal combustion engine and control method therefor

ABSTRACT

An internal combustion engine in which first and second turbochargers are incorporated in series has first and second bypass passages bypassing exhaust turbines of the first and second turbochargers and two opening/closing valves for opening/closing the first and second bypass passages respectively. An exhaust gas heating device for heating exhaust gas being led to an exhaust purifying device from the engine is disposed in an exhaust passage so as to be located upstream of a confluent portion of the exhaust passage and the second bypass passage and downstream of the turbine of the second turbocharger. A valve capable of regulating the flow rate of exhaust gas flowing in the exhaust passage is disposed in the exhaust passage so as to be located downstream of a branched portion of the exhaust passage and the second bypass passage and upstream of the turbine of the second turbocharger.

TECHNICAL FIELD

The present invention relates to an exhaust heating device that increases a temperature of exhaust gas in order to activate an exhaust purifying device and keep the exhaust purifying device in an activated state in an internal combustion engine that is provided with the exhaust purifying device.

BACKGROUND ART

A turbocharger that relatively easily achieves an improvement in output from an internal combustion engine has a tendency to bring about a drop in fuel efficiency at the same time. In recent years, in order to meet the strong demand for an improvement in fuel efficiency of an internal combustion engine incorporating such a turbocharger therein, an internal combustion engine in which two turbochargers having different characteristics are incorporated is proposed in Patent Literature 1 and Patent Literature 2. In either case, there are provided a first turbocharger that mainly functions in a low speed range of the internal combustion engine and a second turbocharger that mainly functions in other speed ranges, the turbochargers being arranged in series or parallel with respect to intake and exhaust passages.

Meanwhile, in order to cope with strict emission standards set for an internal combustion engine, it is necessary to promote the activation of an exhaust purifying device at the start of the internal combustion engine, maintain its activated state during the operation of the engine, and so on. Therefore, Patent Literature 3 and the like have proposed an internal combustion engine in which an exhaust heating device is incorporated in an exhaust passage upstream of an exhaust purifying device. This exhaust heating device generates heated gas in exhaust gas and supplies this generated heated gas to the exhaust purifying device disposed downstream, to thus promote the activation of the exhaust purifying device and maintain its activated state. To do so, the exhaust heating device generally includes a fuel supply valve which supplies fuel to the exhaust passage and an igniter such as a glow plug which heats and ignites the fuel to generate heated gas. Furthermore, there has been also known an exhaust heating device in which a compact oxidation catalytic converter is incorporated in the exhaust passage downstream of the igniter in order to increase the temperature of the heated gas. Although this oxidation catalytic converter has its own heat generation function and a function for reforming fuel to a low-carbon component, it has a structure different from that of an oxidation catalytic converter that is used as a part of the exhaust purifying device.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Laid-Open No. 2008-255902 -   PTL 2: Japanese Patent Laid-Open No. 2009-270470 -   PTL 3: Japanese Patent Laid-Open No. 2006-112401

SUMMARY OF INVENTION Technical Problem

It is evident that in the future, an internal combustion engine that is able to achieve both good output characteristics and fuel efficiency and clean exhaust gas will be important technology. From this viewpoint, it has been construed that an exhaust heating device is further incorporated in an internal combustion engine incorporating the above-described two-stage exhaust turbocharger therein.

In the case of an operating state where an intake flow rate with respect to the internal combustion engine is large in the exhaust heating device disclosed in Patent Literature 3, a flow rate of exhaust gas flowing through an exhaust passage also is relatively increased. Therefore, the fuel that is supplied to the exhaust passage from a fuel supply valve in the exhaust heating device cannot remain around the igniter. Even if the fuel can be ignited, a flame is blown out by the flow of the exhaust gas, and therefore, there is a possibility that unburned fuel flows toward the exhaust purifying device.

On the other hand, in the internal combustion engine in which the two-stage exhaust turbocharger is incorporated, an exhaust flow rate basically tends to become large. Moreover, the exhaust gas passes through each of exhaust turbines of the two turbochargers, and therefore, the temperature of the exhaust gas greatly drops due to the release of the heat to the outside and a heat capacity of the exhaust turbines per se. As a result, the above-described inconvenience more prominently occurs, and therefore, the exhaust heating device can be actuated only at a small exhaust flow rate, such as deceleration of a vehicle.

An object of the present invention is to provide an exhaust heating device capable of stably and continuously igniting fuel in an internal combustion engine incorporating two-stage exhaust turbochargers therein.

Solution to Problem

A first aspect of the present invention is featured by an exhaust heating device for heating exhaust gas being led to an exhaust purifying device from an internal combustion engine having a first bypass passage bypassing an exhaust turbine of a first exhaust turbocharger, a second bypass passage bypassing an exhaust turbine of a second exhaust turbocharger, and two opening/closing valves for opening or closing the first and second bypass passages independently of each other, the first turbocharger and the second turbocharger that is disposed in an exhaust passage so as to be located upstream of the first turbocharger and is used in mainly a lower speed range of the engine, the first and second turbochargers being incorporated in series on the exhaust passage, wherein the exhaust heating device is disposed in the exhaust passage so as to be located upstream of a confluent portion of the exhaust passage and the second bypass passage and downstream of an exhaust turbine of the second turbocharger; and a valve capable of regulating the flow rate of exhaust gas in the exhaust passage is disposed in the exhaust passage so as to be located downstream of a branched portion of the exhaust passage and the second bypass passage and upstream of the turbine of the second turbocharger.

According to the present invention, in the case where the exhaust heating device need be operated, most of the exhaust gas is introduced to the second bypass passage, and then, the opening of the valve is regulated, so that a part of the exhaust gas is introduced to the exhaust heating device through the turbine of the second turbocharger. Heated gas generated by the operation of the exhaust heating device is converged with the exhaust gas flowing in the second bypass passage at the confluent portion of the exhaust passage and the second bypass passage, and then, flows into the exhaust purifying device.

The exhaust heating device for the engine according to the present invention may include a fuel supply valve for supplying fuel to the exhaust passage, and ignition means for igniting and conflagrating the fuel supplied from the fuel supply valve to the exhaust passage. In this case, an oxidation catalytic converter may be arranged in the exhaust passage between the ignition means and the exhaust purifying device. Moreover, when the fuel is ignited by using the ignition means, it is preferable that the opening of the valve should be regulated in such a manner that the flow rate of the exhaust gas passing the turbine of the second turbocharger becomes smaller than that of the exhaust gas in the second bypass passage.

A second aspect of the present invention is featured by a control method for the exhaust heating device according to the first aspect of the present invention comprising the steps of: determining whether or not the exhaust purifying device is activated; detecting an engine speed of the engine; setting the opening of the valve based on the detected engine speed of the engine; and driving the valve in such a manner as to achieve a set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device.

According to the present invention, in the case of the operating state in which no exhaust gas need be introduced to the second turbocharger, for example, in the case where the engine is out of a low speed region, the opening of the valve that is closed is regulated so as to introduce the exhaust gas also to the turbine of the second turbocharger at a predetermined flow rate while the exhaust heating device is operated. The resultant heated gas is converged with the exhaust gas flowing in the second bypass passage at the confluent portion of the exhaust passage and the second bypass passage, and then, flows into the exhaust purifying device.

In the control method for the exhaust heating device according to the second aspect of the present invention, the step of driving the valve in such a manner as to achieve the set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device may include a step of driving the second opening/closing valve in such a manner as to turn the second bypass passage into a fully open state.

Advantageous Effects of Invention

According to the present invention, even the engine incorporating the two-stage exhaust turbochargers therein can stably actuate the exhaust heating device by regulating the opening of the valve. In addition, the heated gas can be efficiently mixed with the exhaust gas in the second bypass passage at the confluent portion with the exhaust passage.

In the case where the oxidation catalytic converter is incorporated in the exhaust passage between the ignition means and the exhaust purifying device, the heated gas can be more efficiently increased in temperature.

In the case where the opening of the valve is regulated in such a manner that the flow rate of the exhaust air in the first exhaust passage is smaller than that of the exhaust air in the second exhaust passage, the stable heated gas can be more securely generated.

In the case where the opening of the valve is regulated in such a manner that the flow rate of the exhaust air passing the turbine of the second turbocharger is smaller than that of the exhaust air in the second bypass passage and the ignition means ignites the fuel, the stable heated gas can be more securely generated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram of one embodiment of an exhaust heating device for an internal combustion engine according to the present invention;

FIG. 2 is a control block diagram of main components in the embodiment illustrated in FIG. 1;

FIG. 3 is a graph expressing the relationship between an engine speed and a turbine speed; and

FIG. 4 is a flowchart illustrating control procedures for the exhaust heating device in the embodiment illustrated in FIG. 1.

DESCRIPTION OF EMBODIMENTS

An embodiment in which the present invention is applied to a compression-ignition type internal combustion engine incorporating a series-type two-stage exhaust turbocharger will be explained in detail with reference to FIGS. 1 to 4. The present invention is not, however, limited to the embodiment, and the construction thereof may be freely modified according to required characteristics. The present invention is effectively applied also to a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (Liquefied Natural Gas), or the like is used as fuel to be ignited by a spark plug, for example.

Main components of an engine system in the present embodiment are schematically illustrated in FIG. 1, and the control block thereof is illustrated in FIG. 2, wherein a valve mechanism for intake and exhaust, an EGR system, and the like are omitted for the sake of convenience. An engine 10 in the present embodiment is a compression-ignition multicylinder (four cylinders in the embodiment shown in FIG. 1) internal combustion engine that spontaneously ignites light oil as fuel by injecting the fuel directly into a combustion chamber 12 in a compressed state through a fuel injection valve 11. However, the engine 10 may be a single cylinder internal combustion engine from the viewpoint of the characteristics of the present invention. The amount of fuel supplied to the combustion chamber 12 through the fuel injection valve 11 as well as its injection timing is controlled by an ECU (Electronic Control Unit) 14 based on the position of an accelerator pedal 13 depressed by a driver and the operating state of a vehicle. The position of the depressed accelerator pedal 13 is detected by an accelerator position sensor 15, and the detected information is input into the ECU 14 and used for setting the amount of fuel to be injected from the fuel injection value 11.

An intake pipe 17 that is connected to the engine 10 by way of an intake manifold 16 defines an intake passage 18 together with the intake manifold 16. The intake pipe 17 has a branched portion 20 d and a confluent portion 20 c of an intake bypass pipe 20 defining an intake bypass passage 19 upstream and downstream thereof. That is to say, both ends of the intake bypass pipe 20 are connected to the intake pipe 17 via the branched portion 20 d upstream of the intake passage 18 and the confluent portion 20 c downstream of the intake passage 18. In other words, a portion of the intake pipe 17 that is located between the branched portion 20 d and the confluent portion 20 c is arranged in parallel to the intake bypass passage 20. Hereinafter, the intake passage 18 upstream of the branched portion 20 d is called a first intake passage 18 f for the sake of convenience, and further, a portion defined by the intake pipe 17 that is located between the branched portion 20 d and the confluent portion 20 c is called a second intake passage 18 s for the sake of convenience.

An airflow meter 20 and an intake temperature sensor 21 are disposed in the intake pipe 17 further upstream of the branched portion 20 d. Pieces of information related to an intake flow rate and an intake temperature that are detected by the airflow meter 20 and the intake temperature sensor 21, respectively, are input into the ECU 14. The ECU 14 corrects the amount of fuel injected from the fuel injection valve 11 based on the information detected by the airflow meter 20 and the intake temperature sensor 21.

An intercooler 23 that cools intake air in order to increase the filled density of the intake air flowing through the intake passage 18 and a throttle valve 24 that adjusts the opening of the intake passage 18 are provided in the intake pipe 17 further downstream of the confluent portion 20 c. The throttle valve 24 in the present embodiment is electrically connected to the accelerator pedal 13 such that the opening of the intake passage 18 is corrected by the ECU 14 according to the operating state of the vehicle with respect to the position of the accelerator pedal 13 whose position is adjusted by the driver. Here, a throttle valve 24 that is mechanically connected to the accelerator pedal 13 may be adopted such that the opening of the intake passage 18 accurately corresponds to the position of the accelerator pedal 13.

In the intake bypass pipe 20 is disposed an intake bypass valve 25 for opening or closing the intake bypass passage 19. To the intake bypass valve 25 is connected a bypass valve driving motor 26. The ECU 14 controls the operation of the bypass valve driving motor 26 according to the operating state of the vehicle so as to switch the opening or closing operation of the intake bypass valve 25.

An exhaust pipe 28 that defines an exhaust passage 27 has a branched portion 30 d and a confluent portion 30 c of a first exhaust bypass pipe 30 defining a first exhaust bypass passage 29 upstream and downstream thereof. That is to say, both ends of the first exhaust bypass pipe 30 are connected to the exhaust pipe 28 at the branched portion 30 d upstream of the exhaust passage 27 and the confluent portion 30 c downstream of the exhaust passage 27. In other words, a portion (hereinafter this portion is referred to as a first exhaust passage 27 f for the sake of convenience) of the exhaust pipe 27 that is located between the branched portion 30 d upstream of the exhaust passage 27 and the confluent portion 30 c downstream of the exhaust passage 27 is arranged in parallel to the first exhaust bypass passage 29. In the first exhaust bypass pipe 30 is disposed a first exhaust bypass valve 31 for opening or closing the first exhaust bypass passage 29. The ECU 14 is adapted to control the opening or closing operation based on the operating state of the vehicle. To the first exhaust bypass valve 31 in the present embodiment is connected the bypass valve driving motor 26 together with the intake bypass valve 25. The first exhaust bypass passage 29 is designed to be opened or closed in substantially reverse association with the opening or closing operation of the intake bypass valve 25. Here, an individual actuator may be connected to the first exhaust bypass valve 31 so as to open or close the first exhaust bypass passage 29 independently of the intake bypass valve 25.

The exhaust pipe 28 that is located further upstream of the branched portion 30 d of the first exhaust bypass pipe 30 further includes a branched portion 33 d and a confluent portion 33 c of a second exhaust bypass pipe 33 defining a second exhaust bypass passage 32 upstream and downstream thereof, respectively. That is to say, both ends of the second exhaust bypass pipe 33 are connected to the exhaust pipe 28 via the branched portion 33 d upstream of the exhaust passage 27 and the confluent portion 33 c downstream thereof. In other words, a portion (hereinafter this portion is referred to as a second exhaust passage 27 s for the sake of convenience) of the exhaust pipe 27 that is located between the branched portion 33 d upstream of the exhaust passage 27 and the confluent portion 33 c downstream of the exhaust passage 27 is arranged in parallel to the second exhaust bypass passage 32. In the second exhaust bypass pipe 33 is disposed a second exhaust bypass valve 34 for opening or closing the second exhaust bypass passage 32. The ECU 14 controls the opening or closing operation of the second exhaust bypass valve 34 based on the operating state of the vehicle. In the present embodiment, a second bypass valve driving motor 35 is connected to the second exhaust bypass valve 34 so as to control the opening or closing operation of the second exhaust bypass valve 34 via the second bypass valve driving motor 35.

A first turbocharger 36 is arranged so as to span between the first intake passage 18 f and the first exhaust passage 26 f, wherein its compressor 36 a is located in the first intake passage 18 f whereas its exhaust turbine 36 b is located in the first exhaust passage 27 f. Consequently, the first exhaust bypass passage 29 branched from the first exhaust passage 27 f at the branched portion 30 d merges with the exhaust passage 27 at the downstream confluent portion 30 c together with the first exhaust passage 27 f while bypassing the exhaust turbine 36 b of the first turbocharger 36. Moreover, a second turbocharger 37 that is mainly used in the low speed range of the engine 10 more than the first turbocharger 36 is arranged so as to span between the second intake passage 18 s and the second exhaust passage 27 s. A compressor 37 a of the second turbocharger 37 is located in the second intake passage 18 s. In the meantime, an exhaust turbine 37 b of the second turbocharger 37 is located in the second exhaust passage 27 s defined by the second exhaust bypass pipe 33. Therefore, the second exhaust bypass passage 32 branched from the second exhaust passage 27 s at the branched portion 33 d merges with the exhaust passage 27 further upstream of the branched portion 30 d together with the second exhaust passage 27 s at the downstream confluent portion 33 c while bypassing the exhaust turbine 37 b of the second turbocharger 37.

To the exhaust pipe 28 that is located downstream of the confluent portion 30 c with the first exhaust bypass pipe 30 is connected an exhaust purifying device 38 for rendering hazardous substances produced by combustion of an air-fuel mixture inside of the combustion chamber 12 harmless. The exhaust purifying device 38 in the present embodiment is provided with an oxidation catalytic converter 39, a tertiary catalyst, and a NO_(x) catalyst in order upstream of the exhaust passage 27. Here, only the oxidation catalytic converter 39 provided most upstream is illustrated for the sake of convenience. The oxidation catalytic converter 39 incorporates therein a catalyst temperature sensor 40 for outputting a detected temperature (hereinafter referred to as a catalyst temperature) T_(n) of the oxidation catalytic converter 39 to the ECU 14.

In the second exhaust passage 27 s upstream of the exhaust turbine 37 b of the second turbocharger 37 and downstream of the branched portion 33 d of the second exhaust bypass pipe 33 is disposed a flow regulating valve 41 capable of regulating the flow rate of exhaust air in the second exhaust passage 27 s. Moreover, to the flow regulating valve 41 is connected a valve opening sensor 42 for detecting the opening of the flow regulating valve 41. Information detected by the valve opening sensor 42 is designed to be input into the ECU 14. To the flow regulating valve 41 is connected a regulation valve driving motor 43 whose operation is controlled by the ECU 14. Therefore, the opening of the flow regulating valve 41 is regulated based on the operating state of the vehicle and information detected by the valve opening sensor 42.

Incidentally, the opening or closing operation of the second exhaust bypass valve 34 by the second bypass valve driving motor 35 is designed to be basically driven inversely to the opening or closing operation of the flow regulating valve 41. More specifically, only in the case of the fully opened state of the flow regulating valve 41, the second exhaust bypass valve 34 is kept in the fully closed state. To the contrary, in the case where exhaust air is introduced onto the second exhaust bypass passage 27 s, the openings of the second exhaust bypass valve 34 and the flow regulating valve 41 are controlled so as to achieve a required turbocharging pressure.

An exhaust heating device 44 is incorporated in the second exhaust passage 27 s downstream of the exhaust turbine 37 b of the second turbocharger 37 and upstream of the confluent portion 33 c of the second exhaust bypass pipe 33. The exhaust heating device 44 is adapted to produce heated gas, supply it to the exhaust purifying device 38 disposed downstream, activates it, and maintains its activated state. The exhaust heating device 44 in the present embodiment is provided with a fuel supply valve 45, a glow plug 46 serving as igniting means according to the present invention, and an auxiliary oxidation catalytic converter 47 in this order from upstream.

The fuel supply valve 45 is adapted to supply the fuel into the second exhaust passage 27 s. The ECU 14 controls supply timing and supply amount based on whether or not the exhaust purifying device 38 is activated and the vehicle is operated. The operation of supplying the fuel from the fuel supply valve 45 into the second exhaust passage 27 s is performed when the exhaust purifying device 38 is inactive. Consequently, even when it is unnecessary to introduce the exhaust gas to the second exhaust passage 27 s, that is, to make the second turbocharger 37 function, the exhaust heating device 44 is operated, as required. On the other hand, even when the exhaust gas is introduced to the second exhaust passage 27 s so as to make the second turbocharger 37 function, the exhaust heating device 44 is operated, as required.

The glow plug 46 is designed to ignite the fuel that is supplied from the fuel supply valve 45 into the second exhaust passage 27 s and cannot be spontaneously ignited. A direct-current power supply and a booster circuit, not illustrated, are connected to the glow plug 46 in order to supply power to the glow plug 46. The surface temperature of the glow plug 46 is controlled by the ECU 14. The glow plug 46 may be replaced with a ceramic heater or the like as the igniting means according to the present invention.

The auxiliary oxidation catalytic converter 47 is disposed in the exhaust passage 27 between the glow plug 46 and the exhaust purifying device 38. Although the auxiliary oxidation catalytic converter 47 is disposed on the second exhaust passage 27 s upstream of the confluent portion 33 c in the present embodiment, it may be disposed on the exhaust passage 27 downstream of the confluent portion 33 c. The auxiliary oxidation catalytic converter has a smaller cross-sectional area than that of the second exhaust passage 27 s, and therefore, enables a part of exhaust gas not to pass therethrough. That is to say, the flow rate of the exhaust gas passing the auxiliary oxidation catalytic converter 47 is lower than that of the exhaust gas that does not pass there, so that the temperature of the exhaust gas passing the auxiliary oxidation catalytic converter 47 can be further increased. When the auxiliary oxidation catalytic converter 47 is satisfactorily increased in temperature, that is, activated, power to the glow plug 46 can be cut so as to directly burn the air-fuel mixture inside of the auxiliary oxidation catalytic converter 47. However, when the auxiliary oxidation catalytic converter 47 is not activated, such as at the time of the cold start of the engine 10, it is necessary to supply power to the glow plug 46. When the temperature of the auxiliary oxidation catalytic converter 47 becomes high, hydrocarbons having a large carbon number in an unburned air-fuel mixture are decomposed so as to be reformed into highly reactive hydrocarbons having a small carbon number. In other words, on one hand, the auxiliary oxidation catalytic converter 47 functions as a rapid heat generating element that generates heat at a high speed per se, and on the other hand, also functions as a fuel reforming catalyst that generates reformed fuel. In the present embodiment, there is provided an auxiliary temperature sensor 48 that detects the temperature of the auxiliary oxidation catalytic converter 47 (hereinafter referred to as an auxiliary catalyst temperature) T_(Sn) and outputs it to the ECU 14. Thereafter, the ECU 14 determines based on the information detected by the auxiliary temperature sensor 48 whether or not the power is supplied to the glow plug 46.

In this manner, heated gas is generated on the second exhaust passage 27 s, and the high-temperature exhaust gas passes the auxiliary oxidation catalytic converter 47 so that its temperature is further increased, and the unburned gas is burned by the auxiliary oxidation catalytic converter 47 or is reformed into highly active hydrocarbons. And then, these kinds of gas are mixed with the exhaust gas flowing in the second exhaust bypass passage 32 at the confluent portion 33 c, to be thus supplied toward the exhaust purifying device 38. As a result, it is possible to quickly activate the exhaust purifying device 38 and maintain its activated state even while the vehicle travels.

Incidentally, in order to enhance the ignitability of the fuel that is injected from the fuel supply valve 45 into the second exhaust passage 27 s, it is effective to provide a plate-shaped vaporization promoting member in such a manner as to face the fuel supply valve 45 and the glow plug 46. This vaporization promoting member has the function of scattering and atomizing fuel, or promoting vaporization of the fuel when the fuel injected from the fuel supply valve 45 collides therewith.

The characteristics of the first and second turbochargers 36 and 37 in the present embodiment are illustrated in FIG. 3. The first turbocharger 36 that has a relatively large inertia mass hardly has any supercharging ability in a range in which an engine speed, that is, an engine speed N_(n) per unit time is less than a predetermined speed N_(R) (hereinafter referred to as a turbocharged state determining speed). That is to say, the first turbocharger 36 exhibits the supercharging ability in the range in which the engine speed N_(n) is higher than and equal to the turbocharged state determining speed N_(R). In contrast, the second turbocharger 37 that has a relatively small inertia mass is designed to exhibit the supercharging ability in the range of the low engine speed in which the first turbocharger 36 cannot function. Consequently, the ECU 14 actuates the second turbocharger 37 without actuating the first turbocharger 36 in the case where the engine speed N_(n) is lower than the turbocharged state determining speed N_(R). Specifically, the ECU 14 maintains the first exhaust bypass valve 31 and the flow regulating valve 41 in basically substantially the fully open state whereas maintains the intake bypass valve 25 and the second exhaust bypass valve 34 in the fully closed state. In contrast, the ECU 14 actuates the first turbocharger 36 without actuating the second turbocharger 37 in the case where the engine speed N_(n) is higher than and equal to the turbocharged state determining speed N_(R). Specifically, the ECU 14 maintains the exhaust bypass valve 31 and the flow regulating valve 41 in the fully closed state whereas maintains the intake bypass valve 25 and the second exhaust bypass valve 34 in basically substantially the fully open state. In this manner, the crank angle sensor 49 detects the crank angle phase of the engine 10, and then, inputs the detected information into the ECU 14. The ECU 14 calculates the engine speed N_(n) based on the information output from the crank angle sensor 49.

When it is necessary to supply fuel from the fuel supply valve 45 to the second exhaust passage 27 s so as to activate the exhaust purifying device 38, only a part of the exhaust gas is allowed to flow in the second exhaust passage 27 s. Specifically, the flow regulating valve 41 is slightly closed in the fully open state or is slightly opened in the fully closed state, and further, the opening of the second exhaust bypass valve 34 is controlled in such a manner that the exhaust gas is introduced in the amount to be supplied to the second exhaust passage 27 s. In this manner, the fuel to be injected from the fuel supply valve 45 to the second exhaust passage 27 s is ignited by the glow plug 46, and thus, is turned into heated gas without any extinguishing. The heated gas is mixed with the exhaust gas flowing from the second exhaust bypass passage 32 at the confluent portion 33 c to the second exhaust bypass pipe 33. This promotes the activation of the exhaust purifying device 38.

The ECU 14 controls the actuation of the intake bypass valve 25, the first and second exhaust bypass valves 31 and 34, the flow regulating valve 34, and the exhaust heating device 44, that is, the fuel supply valve 45 and the glow plug 46. The control with respect to these members is performed in accordance with a preset program based on the operating state of the vehicle and detection signals from the auxiliary temperature sensor 48 and the catalyst temperature sensor 40, as follows. Specifically, when the temperature T_(n) of the oxidation catalytic converter 39 is lower than a temperature (hereinafter referred to as an activation index temperature) T_(R) as the index of its activation based on the detection signal from the catalyst temperature sensor 40, it is determined that the exhaust purifying device 38 is not activated, thus actuating the exhaust heating device 44. In contrast, when the catalyst temperature T_(n) is higher than and equal to the activation index temperature T_(R), it is determined that the exhaust purifying device 38 is activated, thus stopping the actuation of the exhaust heating device 44. Moreover, when the temperature T_(Sn) of the auxiliary oxidation catalytic converter 47 is lower than a temperature (hereinafter referred to as an activation index temperature) T_(SR) as the index of its activation, it is determined that the auxiliary oxidation catalytic converter 47 is not activated, thus supplying the power to the glow plug 46. In contrast, when the auxiliary catalyst temperature T_(Sn) is higher than and equal to the activation index temperature T_(SR), it is determined that the auxiliary oxidation catalytic converter 47 is activated, thus stopping the power supply to the glow plug 46. In the meantime, in the case where the exhaust heating device 44 is actuated in the state in which the engine speed N_(n) is higher than and equal to the turbocharged state determining speed N_(R), the flow regulating valve 41 in the fully closed state is just maintained in a slightly open state. That is to say, the intake bypass valve 25 and the second exhaust bypass valve 34 can remain in the fully open state whereas the first exhaust bypass valve 31 can remain in the fully closed state. In this manner, a part of the exhaust gas is introduced to the second exhaust passage 27 s, thus igniting the fuel and preventing any extinguishing (exemplified by characteristics indicated by an arrow A in FIG. 3). In contrast, it is possible that the fuel cannot be ignited or is extinguished when the intake bypass valve 25 and the second exhaust bypass valve 34 remain in the fully closed state whereas the first exhaust bypass valve 31 and the flow regulating valve 41 remain in the fully open state in the case where the engine speed N_(n) is lower than the turbocharged state determining speed N_(R). In this case, the flow regulating valve 41 in the fully open state remains in a slightly open state and the opening of the second exhaust bypass valve 34 in the fully closed state is controlled in such a manner that the exhaust gas is introduced in the amount to be supplied to the second exhaust passage 27 s. As a consequence, most of the exhaust gas is introduced to the second exhaust bypass passage 32, so that the fuel to be supplied to the second exhaust passage 27 s cannot be extinguished (exemplified by characteristics indicated by an arrow B in FIG. 3).

In this manner, the opening of the flow regulating valve 41 is regulated in such a manner as not to extinguish the fuel to be supplied to the second exhaust passage 27 s from the fuel supply valve 45 in the above-described exhaust heating device 44. In other words, the flow rate of the exhaust gas to be introduced into the second exhaust passage 27 s is smaller than that of the exhaust gas flowing in the second exhaust bypass passage 32. More particularly, the ECU 14 sets the opening of the flow regulating valve 41 via the regulation valve driving motor 43 such that the exhaust gas flows in the second exhaust passage 27 s in such a flow rate as not to extinguish a flame generated by the ignition of the fuel inside of the second exhaust passage 27 s. In this manner, the exhaust gas at the predetermined flow rate that cannot extinguish a flame can flow in the second exhaust passage 27 s, and therefore, the heated gas obtained by the exhaust heating device 44 can be introduced to the exhaust purifying device 38.

A control procedure of the above-described exhaust heating device 44 is illustrated in a flowchart in FIG. 4. Specifically, it is determined in step S11 whether or not the temperature T_(n) of the oxidation catalytic converter 39 that is detected by the catalyst temperature sensor 40 is lower than the activation index temperature T_(R). Here, when it is determined that the exhaust heating device 44 need not be actuated since the catalyst temperature T_(n) is higher than or equal to the activation index temperature T_(R), that is, the oxidation catalytic converter 39 is activated, the determining processing in step S11 is repeated without performing any processing. In contrast, when it is determined in step S11 that the catalyst temperature T_(n) is lower than the activation index temperature T_(R), that is, the oxidation catalytic converter 39 is not activated so that the exhaust heating device 44 need be actuated, the control routine proceeds to step S12. In step S12, it is determined whether or not the temperature T_(Sn) of the auxiliary oxidation catalytic converter 47 to be detected by the auxiliary temperature sensor 48 is lower than the activation index temperature T_(SR). Here, the auxiliary catalyst temperature T_(Sn) is lower than the activation index temperature T_(SR), that is, the auxiliary oxidation catalytic converter 47 remains inactivated. Therefore, in the case where it is determined that the power need be supplied to the glow plug 46, the control routine proceeds to step S13. In step S13, it is determined whether or not a flag for supplying the power to the glow plug 46 is set. Since at first, the flag is not set, the control routine proceeds to step S14 in which the flag is set, and further, the power is supplied to the glow plug 46 in step S15. Furthermore, in step S15, the intake bypass valve 25, the first and second exhaust bypass valves 31 and 34, and the flow regulating valve 41 are opened or closed based on the engine speed N_(n).

For example, in the case where the engine speed N_(n) is lower than the turbocharged state determining speed N_(R), the intake bypass valve 25 and the second exhaust bypass valve 34 are fully closed whereas the first exhaust bypass valve and the flow regulating valve 41 are fully opened. Consequently, the openings of the flow regulating valve 41 and the second exhaust bypass valve 34 are controlled such that the fuel supplied to the second exhaust passage 27 s flows at such a flow rate as not to extinguish the flame when the fuel is ignited by the flow plug 46. More specifically, the flow regulating valve 41 is closed in the fully open state, and further, the opening of the second exhaust bypass valve 34 is controlled, so that the exhaust gas is introduced to the second exhaust passage 27 s in the necessary amount. In this manner, the amount of the exhaust gas flowing in the second exhaust passage 27 s is reduced whereas the residual exhaust gas is introduced to the first exhaust bypass passage 32. In contrast, in the case where the engine speed N_(n) is higher than and equal to the turbocharged state determining speed N_(R), the intake bypass valve 25 and the second exhaust bypass valve 34 are fully open whereas the first exhaust bypass valve 31 and the flow regulating valve 41 are fully closed. Consequently, the flow regulating valve 41 is slightly opened in the fully closed state in such a manner as to ignite the fuel supplied to the second exhaust passage 27 s, so that a part of the exhaust gas is introduced also to the second exhaust passage 27 s.

Next, the fuel is injected from the fuel supply valve 45 toward the second exhaust passage 27 s in step S17. In this manner, the fuel is ignited on the second exhaust passage 27 s, on which the exhaust gas slightly flows, and further, the resultant heated gas is further increased in temperature by the auxiliary oxidation catalytic converter 47. The heated gas is mixed with the exhaust gas flowing at the confluent portion 33 c to the first exhaust bypass passage 32, and then, is introduced to the exhaust purifying device 38 whose temperature is increased. Subsequently, it is determined in step 18 whether or not the catalyst temperature T_(n) detected by the catalyst temperature sensor 40 is higher than and equal to the activation index temperature T_(R). Here, the catalyst temperature T_(n) is lower than the activation index temperature T_(R), that is, the oxidation catalytic converter is inactive. Therefore, in the case where it is determined that the operation of the exhaust heating device 44 need be continued, the control routine returns to step S12, and therefore, the foregoing processing is repeated. In contrast, in the case where it is determined that the actuation of the exhaust heating device 44 need be stopped since the catalyst temperature T_(n) is higher than and equal to the activation index temperature T_(R), that is, the oxidation catalytic converter 39 becomes active, the control routine proceeds to step S19. In step S19, it is determined whether or not the flag is set. When the flag is determined to be set, the power supply to the glow plug 46 is stopped in step S20, and then, the flag is reset in step S21. Thereafter, the fuel supply from the fuel supply valve 45 is stopped in step S22, and further, the valve opening control is ended in step S16. Hence, the control routine returns to the determination in step S11. In this manner, the intake bypass valve 25, the first and second exhaust bypass valves 31 and 34, and the flow regulating valve 41 can be controlled to be opened or closed such that the first and second turbochargers 36 and 37 can be most efficiently operated according to the engine speed N_(n).

On the other hand, in the case where it is determined that the flag is set in the previous step S13, that is, the power is supplied to the glow plug 46, the control routine jumps to step S16, thus continuing the operation of the exhaust heating device 44.

Moreover, since the auxiliary catalyst temperature T_(Sn) is higher than and equal to the activation index temperature T_(SR) in the previous step S12, that is, the auxiliary oxidation catalytic converter 47 is active, the control routine proceeds to step S23 when it is determined that the power need not be supplied to the glow plug 46. It is determined in step S23 whether or not the flag is set. In the case where it is determined that the flag is set, that is, the power is supplied to the glow plug 46, the control routine proceeds to step S24 where the power supply to the glow plug 46 is stopped. Next, the flag is reset in step S21. Thereafter, the control routine proceeds to the previous step S16, thus continuing the operation of the exhaust heating device 44. In contrast, when it is determined that the flag is not set in step S23, that is, no power is supplied to the glow plug 46, the control routine jumps to step S16, thus continuing the operation of the exhaust heating device 44.

Incidentally, when no problem arises even though the fuel injected from the fuel supply valve 45 to the second exhaust passage 27 s is extinguished, it should be understood that the exhaust heating device 44 can be actuated in an arbitrary operating state.

It is to be noted that the present invention shall be construed solely from the matters described in the claims thereof, and the foregoing embodiment includes not only the matters described above but any modifications and alterations encompassed by the concept of the present invention. In other words, all the matters in the foregoing embodiment are not to limit the present invention, but include any configurations which may be directly irrelevant to the present invention and can be optionally changed according to the usage, purpose, and the like.

REFERENCE SIGNS LIST

-   10 Engine -   11 Fuel injection valve -   12 Combustion chamber -   13 Accelerator pedal -   14 ECU -   15 Accelerator position sensor -   16 Intake manifold -   17 Intake pipe -   18 Intake passage -   18 f First intake passage -   18 s Second intake passage -   19 Intake bypass passage -   20 Intake bypass pipe -   20 d Branched portion -   20 c Confluent portion -   21 Airflow meter -   22 Intake temperature sensor -   23 Intercooler -   24 Throttle valve -   25 Intake bypass valve -   26 Bypass valve driving motor -   27 Exhaust passage -   27 f First exhaust passage -   27 s Second exhaust passage -   28 Exhaust pipe -   29 First exhaust bypass passage -   30 First exhaust bypass pipe -   30 d Branched portion -   30 c Confluent portion -   31 First exhaust bypass valve -   32 Second exhaust bypass passage -   33 Second exhaust bypass pipe -   33 d Branched portion -   33 c Confluent portion -   34 Second exhaust bypass valve -   35 Second bypass valve driving motor -   36 First turbocharger -   36 a Compressor -   36 b Exhaust turbine -   37 Second turbocharger -   37 a Compressor -   37 b Exhaust turbine -   38 Exhaust purifying device -   39 Oxidation catalytic converter -   40 Catalyst temperature sensor -   41 Flow regulating valve -   42 Valve opening sensor -   43 Regulation valve driving motor -   44 Exhaust heating device -   45 Fuel supply valve -   46 Glow plug -   47 Auxiliary oxidation catalytic converter -   48 Auxiliary temperature sensor -   49 Crank angle sensor -   N_(n) Engine speed -   N_(R) Turbocharged state determining speed -   T_(n) Catalyst temperature -   T_(R) Activation index temperature -   T_(Sn) Auxiliary catalyst temperature -   T_(SR) Activation index temperature 

1-6. (canceled)
 7. An exhaust heating device for heating exhaust gas being led to an exhaust purifying device from an internal combustion engine having a first bypass passage bypassing an exhaust turbine of a first exhaust turbocharger, a second bypass passage bypassing an exhaust turbine of a second exhaust turbocharger, and two opening/closing valves for opening or closing the first and second bypass passages independently of each other, the first exhaust turbocharger and the second exhaust turbocharger that is disposed in an exhaust passage so as to be located upstream of the first turbocharger and is used in mainly a lower speed range of the internal combustion engine, the first and second turbochargers being incorporated in series on the exhaust passage, wherein the exhaust heating device is disposed in the exhaust passage so as to be located upstream of a confluent portion of the exhaust passage and the second bypass passage and downstream of an exhaust turbine of the second turbocharger; and a valve capable of regulating the flow rate of exhaust gas in the exhaust passage is disposed in the exhaust passage so as to be located downstream of a branched portion of the exhaust passage and the second bypass passage and upstream of the exhaust turbine of the second exhaust turbocharger.
 8. The exhaust heating device for the engine as claimed in claim 7, wherein the exhaust heating device includes a fuel supply valve for supplying fuel to the exhaust passage, and ignition means for igniting and conflagrating the fuel supplied from the fuel supply valve to the exhaust passage.
 9. The exhaust heating device for the engine as claimed in claim 8, wherein an oxidation catalytic converter is provided in the exhaust passage between the ignition means and the exhaust purifying device.
 10. The exhaust heating device for the engine as claimed in claim 8, wherein when the fuel is ignited by using the ignition means, the opening of the valve is regulated in such a manner that the flow rate of the exhaust gas passing the exhaust turbine of the second turbocharger becomes smaller than that of the exhaust gas in the second bypass passage.
 11. The exhaust heating device for the engine as claimed in claim 9, wherein when the fuel is ignited by using the ignition means, the opening of the valve is regulated in such a manner that the flow rate of the exhaust gas passing the exhaust turbine of the second turbocharger becomes smaller than that of the exhaust gas in the second bypass passage.
 12. A control method for the exhaust heating device as claimed in claim 7, comprising the steps of: determining whether or not the exhaust purifying device is activated; detecting an engine speed of the engine; setting the opening of the valve based on the detected engine speed of the engine; and driving the valve in such a manner as to achieve a set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device.
 13. A control method for the exhaust heating device as claimed in claim 8, comprising the steps of: determining whether or not the exhaust purifying device is activated; detecting an engine speed of the engine; setting the opening of the valve based on the detected engine speed of the engine; and driving the valve in such a manner as to achieve a set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device.
 14. The control method as claimed in claim 12, wherein the step of driving the valve in such a manner as to achieve the set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device includes a step of driving the second opening/closing valve in such a manner as to turn the second bypass passage into a fully open state.
 15. The control method as claimed in claim 13, wherein the step of driving the valve in such a manner as to achieve the set opening when it is determined that the exhaust purifying device is not activated so as to lead the exhaust gas to the turbine of the second turbocharger at a predetermined flow rate and actuate the exhaust heating device includes a step of driving the second opening/closing valve in such a manner as to turn the second bypass passage into a fully open state. 